The present invention relates to a hub assembly of a rotor for holding at least one wing, wherein the at least one wing is connected/mounted to the hub assembly in at least two suspension points. The hub assembly may be applied to any kind of either energy extracting devices such as wind turbines or the like or lift producing devices such as helicopter rotors or propellers.
The invention is suited for rotors in general and is able to enable coning movement of wings connected/mounted to the hub assembly, enable teetering movement of the rotor and enable alteration of the pitch angle of the wings connected/mounted to the hub assembly. The hub assembly according to the present invention provides a hub where all the pitching of the wings can occur synchronously/simultaneous due to an interconnection of the wings attached/mounted to the hub assembly and that coning of the wings may be applied at the same time with pitching of the wings and teetering of the rotor.
The usual approach to enable at least the pitching movement of the wings connected / mounted to the hub assembly is to mount the wings to the hub assembly by connecting the wing root to the hub via a ball bearing or similar bearing. This connection is usually centred close to the aerodynamic centre of the wing section, i.e. the point where the pitching moment resulting from the aerodynamic load on the wing is substantially zero.
The pitching of wings connected/mounted to the hub assembly in the usual manner is usually enabled by applying transmission system such as gearboxes, hydraulic pistons or the like to rotate the wings along theirs longitudinal direction. These gearboxes must some how be interconnect in order to assure synchronous/simultaneous pitching. Furthermore, the mounting/connection of the wings through wing root bearing or the like makes it very difficult to enable the wings to cone,.as this usually requires very expensive bearing and the application of springs and hydraulic systems to control the coning.
Furthermore, a teetering movement of the rotor is usually avoided even though such a motion is very desirable, as no workable solution has been found until now. A workable solution means that the solution should be strong, some how simple in order to avoid damages and reliable, so that operation of for instance a wind turbine is efficient even during high stress conditions and fatigue loads.
Thus, it is an aim of the present invention to provide a rotor comprising a hub assembly and at least one wing, where the pitch of the wing may be controlled by displacing at least one of at least two suspension point used for connecting I mounting at wing to the hub assembly.
From the prior art, hub assemblies allowing pitching and coning of the wings are known.
On such example is U.S. Pat. No. 4,131,391 which discloses a hub assembly for a helicopter where each wing is connected to the hub assembly via a serial connection comprising a bearing and a hinge. The bearing allows the wing to rotate around it longitudinal direction in order to adjust theirs pitch angle and the hinge allows the wing to cone. The pitch angle o the wings is adjusted by a rod connected to the bearing and acting at the periphery of the bearing in order to provide a lever used for rotating the blade.
A major problem of such known assemblies is that they do not allow the wings to be connected/mounted to the hub assembly in at least two suspensions point as the pitching of the wings is to be performed by rotating the wings in a bearing centred in the aerodynamic centre of the wings, which centering is crucial in the known hub assemblies as minimum pitching torque is indispensable in these cases.
U.S. Pat. No. 4,678,923 discloses a hub assembly for a wind turbine. The wings are connected to the hub by means of at least two resilient strips which are oppositely inclined both in the plane of rotation of the wings and in a plane extending through the rotational axis of the hub. In particular, each wing is connected to flanges of the hub by means of said two resilient strips in the sense that one strip connects the wing with a first flange and the other strip connects the wing with a second flange.
GB 2 029 911 discloses a connection arrangement for connecting a wing having a load bearing shell to a hub of a wind turbine. The arrangement comprises an inner sleeve connected to the hub and an outer sleeve connected to the wing. The wing is being connected to the hub by securing by bolts the inner and the outer sleeves to each other.
A major problem of such known assemblies and arrangements is that pitching of one wing of the rotor is de-coupled from pitching of another wing of the rotor (in the sense that pitching of one wing is not mechanically fed back to other wings) whereby each of the wing may be operating at its own pitch angle.
The present invention provides a novel, simple and effective alternative to known rotors with hub assemblies. The present invention also provides a rotor with hub assembly that, besides from being cheaper than prior art rotors and hub assemblies, also allow the application of wings without the usual applied main spar extending inside wings in theirs entire length, whereby the weight of the wings and thereby the weight of the rotor may be smaller than usual which most often will provide a rotor more efficiently controlled.
Thus, in a first aspect, the present invention relates to a rotor having an axis of rotation said rotor comprising a hub assembly and at least one wing having a leading edge and a trailing edge, said at least one wing being connected/mounted to the hub assembly in at least two suspensions points so that the pitch of the wing may be controlled by displacing at least one of the suspensions points.
The at least one wing connected/mounted to the hub assembly extends from a root section to a tip section, and the wing is preferably connected/mounted to the hub assembly at the root section. By this way of connecting/mounting the wing to the hub assembly, a very advantageous way of controlling the pitch of the at least one wing is provided. As only one of the suspension points need to be displaced the wing does not have be connected I mounted to the hub assembly via a large and expensive ball bearing centred in the Aerodynamic centre of the wing. Furthermore, as only one suspension point needs to be displaced the need for a gearbox or the like used for turning the wing in a ball bearing is also not needed.
Furthermore, by having the two suspension points situated at or in the vicinity of the leading edge and the trailing edge of the wing shell, its torsional stiffness is effectively used to transfer driving torque loads.
A typical displacement of the at least one displacement point is a displacement substantially normal to the plane defined by the rotation of the wing, but the invention is not limited to this situation, as a change of the pitch of the wing may be accomplished by all possible displacements of at least one suspension point as long as such a displacement has a component in the direction normal to the plane defined by the rotation of the wing.
Preferably, the pitch of the at least one wing is controlled by a general mutual relative displacement of the suspension points.
In a preferred embodiment of the present invention, the at least two suspension points are situated/arranged on a circle having its centre in the centre of the axis of rotation of the rotor. In this preferred embodiment of the present invention, the suspension of the wing is neutral in the sense that substantially no interaction is present between a flap load (a load on the wing in the direction of the in going wind) and the pitching of the wing.
Furthermore, the suspension points are in a presently most preferred embodiment arranged in the vicinity of the leading edge and in the vicinity of the trailing edge of the wing. Covered by this situation is also the arrangement where the suspension points in arranged in the leading edge region and/or in the trailing edge region of the wing.
In another preferred embodiment of the present invention, the at least two suspension points are situated/arranged on two circles having different radii and having the same centre, which centre is situated in the centre of the axis of rotation. In this preferred embodiment of the present invention, it is possible to obtain an interaction between a flap load and the pitch angle of the wing, as a flap load, which has a force component normal to a line passing through the at least two suspension points will give rise to change of the pitch of the wing.
Preferably, the hub assembly comprises at least two hub main parts each of which is pivotally connected to a central hub part of the hub assembly so that the at least two hub main parts of the hub assembly may be rotated around an axis being inclined with respect to a longitudinal direction of each of the hub main parts so as to displace at least one of the suspension points whereby the pitch of the at least one wing is altered.
The central hub part of the rotor assembly, typically denotes a teeter shaft, connects in a preferred embodiment of the invention the two hub main parts in such a manner as to allow the two main hub parts to rotate around the longitudinal direction of the teeter shaft. The connection of the hub main parts to the teeter shaft is preferably a rubber bearing or a ball bearing so as to allow the rotation of the hub main parts to rotate around the longitudinal direction of the teeter shaft. Rubber bearings are preferably applied when a stiffness and/or flexibility is needed and ball bearings are preferably applied when low friction connections are needed. Bearings such as roll bearings, bushings or flexible connections made of flexible materials may be used.
In a presently most preferred embodiment of the invention, the pitching of the wing is provided by rotating the two main hub parts in opposite directions substantially asynchronously (when view from one side), whereby the wing attached/connected to the hub main parts at theirs extremities at the suspension points will cause the wing to rotate around its longitudinal direction as these suspension points will be displaced in opposite directions.
In the presently most preferred embodiment of the invention the angle between the central hub part (teeter shaft) and each of the two hub main parts is typically around 90xc2x0 whereby substantially no interaction between a flap load and pitching of the wing is present.
The angle between the central hub part (teeter shaft) and the two hub main parts may preferably be made different from 90xc2x0 in order to provide an interaction between a flap load and pitching of the wing. Preferably angles such as between 90-80xc2x0, and in some situation between 80-70xc2x0, and even angles between 70-60xc2x0 may be preferred, which in some situations is preferred between 60-50xc2x0.
In a preferred embodiment of the present invention the central part of the hub assembly is substantially rigidly connected to a main shaft of the rotor. In such a preferred embodiment a teeter movement, i.e. a motion where the angle between the plane defined by the rotation of the wing (the rotor plane) and for instance the angle of rotation of the rotor may be varied, is provided by synchronous rotation of the two hub main parts around the teeter shaft (the hub central part).
This rigidly connection may also provide a rotor wherein substantially no teeter movement of the rotor is possible. In such a situation the two hub main parts are connected to the hub central part in such a way that only an asynchronous movement of the hub main parts is possible.
In another preferred embodiment of the present invention the central part of the hub assembly is pivotally connected to the main shaft so as to allow the angle between the plane defined by the sweeping motion of the at least one wing upon rotation and the axis of rotation of the main shaft to be a geometrical degree of freedom, which movement is typically denoted a teeter movement of the rotor.
In this embodiment the connection of the hub central part to the main shaft may be provided by a hinge, whereby the teeter movement of the rotor is provided at the same time as the torque produced by the rotor can be transferred to the main shaft of the rotor.
This way of hinging the hub central part to the main shaft of the rotor may advantageous be combined with the above described connection of the two hub main parts to the hub central part allowing the rotor to teeter or the connection disabling a synchronous movement of the two main hub parts. In the first case the teeter movement of the rotor is possible as more than one connection provides a very flexible rotor and in the second case, the teeter movement of the rotor is provided by only one connection whereby a more easy control of the teeter movement may be possible.
In the presently most preferred embodiment of the present invention, each of the hub main parts is pivotally connected to a central part of the hub assembly in such a manner that the at least two main parts of the hub assembly may be rotated synchronously/simultaneously around an axis being inclined with respect to the longitudinal direction of each of the hub main parts so as to allow the angle between the plane defined by the sweeping motion of the at least one wing upon rotation and the axis of rotation of the main shaft to be a geometrical degree of freedom
In the presently most preferred embodiment of the present invention the hub assembly further comprises connecting means/mounting means arranged at each suspension point for hingedly connecting/mounting the at least one wing to the hub main parts so as to allow the angle between the longitudinal extension of the wing and the axis of rotation of the rotor to be a geometrical degree of freedom whereby the wing may cone.
Such a coning of the wing is very advantageous as such a movement of the wing may reduce the axial thrust and flapwise load or may be used for controlling the torque applied from the rotor to the main shaft in case the rotor is an energy-extracting rotor. When maximum torque is to be reduced the wings may be coned. Such a coning may be controlled actively or it may be the result of the load on the wing or a combination of both. In a preferred embodiment of the present invention the hub assembly further comprises means for controlling the coning of the at least one wing whereby the coning of the wing may be made different from the coning occurring as an interaction between the centrifugal force produced by the rotation of the wing and the aerodynamic loads on the wings.
These means for controlling the coning of the wing may preferably be provided by applying a stiffness to the connecting/mounting means, which may for instance be provided by applying connecting/mounting means made of an indulgent material such as rubber or a composite or the like. It should be noted, that combinations of mounting means being constituted by bearings and means made of an indulgent material may be applied according to the present invention in order to control the coning movement of the wings.
In one embodiment of the present invention the coning controlling means is a flex-beam made of a flexible material, which beam is attached to at least the root section of the at least one wing and to the hub assembly which also preferably may be combined with the above described connecting/mounting means.
This flex-beam will provide, due to its stiffness, stiffness to the coning movement of the wing. When the wing starts to cone the flex-beam will have to bend as the flex-beam is connected to the wing and hub assembly. The flex-beam may preferably also serve the purpose of controlling the maximum coning of the wing. Such a control is very advantageous for instance when the rotor is situated upstream for instance a tower of a wind turbine. In this situation, it is crucial to be able to control the coning in order to assure that a wing does not hit the tower when it cone.
The flex-beam may preferably be an integral part of the wing and the flex-beam may preferably be connected to the hub assembly via a hydraulic means, such as a hydraulic piston, in order to provide a control of the coning movement of the wing. The hydraulic means may in this embodiment of the invention then make it possible to control the coning of the wing and at the same time have a flex-beam which balances the aerodynamic load on the wing.
In an embodiment not having a flex-beam, the coning of the wing may be provided and controlled by a coning controlling means which preferably may be a hydraulic means connected to a wing and to the hub assembly. Such a coning controlling means may, of course, be combined with a flex-beam.
In a presently most preferred embodiment of the present invention the rotor has at least two wings, and the hub assembly further comprises at least one auxiliary part having a crossbeam extending from one hub main part to a position where another hub main part of the rotor assembly is connected to the hub central part. This connection may preferably be constituted by use of bearings such as rubber bearings, ball bearings or flexible connections.
By applying such and auxiliary part to the hub main parts, the stiffness of the hub main parts may be improved and the forces applied to the each of the bearings through which the hub main parts are connected to the teeter shaft may in this embodiment be lowered as the forces now may be distributed to more bearings.
The hub assembly may in this preferred embodiment further comprise at least one support member extending from one hub main part to the crossbeam extending from the same hub main part. This at least one support member may provide a further stiffness to the hub assembly and furthermore serve as an attachment member where each of the flex-beams of each wing is connected to.
In a preferred embodiment of the present invention the auxiliary part is an integral part of each of the hub main parts, which preferably is triangular shaped.
The hub assembly further comprises means for controlling the pitch of the wing. The pitch controlling means is used for rotating the two hub main parts of the hub assembly synchronous in order to displace the at least two suspension point in opposite direction so as to alter the pitch of the wing attached/connected to the two hub main parts.
In order to provide an opposite displacement of the two suspension points in which each wing is connected X attached to the hub assembly and at the same time allowing the rotor to teeter, the pitch controlling means is preferably a hydraulic piston connected at one end to one hub main part and at the other end to another hub main part. The position in which the pistonxe2x80x94or other similar means for adjusting the pitch xe2x80x94is connected to the hub main parts must be elevated with respect to a line passing through two corresponding suspension points of two wings in order to provide the possibility of decreasing/increasing the direct distance between such two suspension point, which decrease/increase is needed in order to displace the suspension points.
In preferred embodiments wherein the teeter movement of the rotor is provided by for instance a hinge for hinging the central part of the hub assembly to the main shaft of the rotor or where no teeter movement is provided, the pitch controlling means may preferably be a hydraulic piston connected at one end to the central part of the hub assembly and at the other end to a hub main part.
In a presently most preferred embodiment of the present invention the rotor comprises at least two wings, and each of the hub main parts extends at least from one suspension point arranged substantially in the vicinity of the leading edge of the root section of one wing pass the hub central part and to another suspension point arranged substantially in the vicinity of the trailing edge of the root section of another wing.
The wording substantially in the vicinity of the leading edge and trailing edge covers also the situation where the position where the suspension points is arranged in the leading and trailing edge region of the wing.
A very advantageous and desirable interaction between pitching of the wings is provided, by extending the hub main parts from one wing to another. As the wings so are interconnected a change of the distance between a suspension point situated in the vicinity of the leading edge of a first wing and a suspension point situated in the vicinity of the leading edge of a second wing will change the pitch of both wings synchronously.
Furthermore, the teeter movement of the rotor may be provided and may be uncoupled from the pitching movement of the wings in this preferred embodiment of the invention when the hub main parts are connected to the hub central part through bearing. This teetering movement may preferably be controlled by providing the hub assembly a teeter stiffness for controlling the teeter motion of each of the at least one wing, for instance provided by the bearings through which the hub main parts are connected to the hub central part which in such a situation preferably are rubber bearings and wherein the teeter stiffness is provided by at least one of the rubber bearings.
Preferably each of the at least one wing(s) is(are) connected/mounted to the hub main parts at the suspension points by use of spherical bearings. By use of spherical bearings two geometrical degrees of freedom are provided, which degrees of freedom are very advantageous as pitching of wings requires one degree of freedom and as a coning of the wings also requires one degree of freedom.
The hub assembly described above, may very advantageous be applied for a rotor comprises three wings and is in the presently most preferred embodiment of the present invention applied in a rotor configuration comprising two wings.
Another very important and advantageous aspect of the present invention relates to a wing having a load-bearing shell. In the presently most preferred embodiment of the invention, the wing having a load bearing shell is applied for a rotor of a wind turbine, but the wing may be applied to all kind of rotors, specially when the wing is connected/mounted to a hub assembly by use of at least two suspension points.
The wing having a load-bearing shell according to the present invention, is preferably applied in a rotor assembly wherein each wing of the rotor assembly is connected/mounted to the hub assembly in two suspension points, which suspension points is preferably situated in the vicinity of respectively the leading edge and the trailing edge of the wings. The load bearing shell transfers the aerodynamic loads acting on the shell to the suspension points.
The load bearing shell is preferably made of reinforced plastic or the like or a metal sheet or the like and forms the aerodynamic share and the interior of the wing is preferably hollow or made of foam.
Preferably the wing comprises two means for connecting/mounting for connecting/mounting the wing to a hub. These connecting/mounting means may preferably be a part of for instance a spherical bearing used in order to provide either one or two degrees of freedom.
As the loads on the wings are transferred to the leading and trailing edge of the wing, the wing may preferably be reinforced in the vicinity of the connecting means I mounting mean, and in such a preferred embodiment of the wing according to the present invention the connecting means/ mounting means are preferably arranged in the vicinity of the leading edge.